Ozone (O 3 ) in upper atmosphere blocks ultraviolet (UV) light from Sun. UV causes skin cancer and cataracts.

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Esmond West
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1 Unit 9: The Gas Laws The Atosphere an ocean of gases ixed together Coposition nitrogen (N ) ~78% oxygen (O ).~% argon (Ar).~0.93% carbon dioxide (CO )..~0.03% water apor (H O) ~0.% Trace aounts of: He, Ne, Rn, SO, CH 4, N x O x, etc. Depletion of the Ozone Layer Ozone (O 3 ) in upper atosphere blocks ultraiolet (U) light fro Sun. U causes skin cancer and cataracts. O 3 depletion is caused by chlorofluorocarbons (CFCs). Uses for CFCs: refrigerants aerosol propellants CFCs banned in U.S. in 996 O 3 is replenished with each strike of lightning.

2 The Greenhouse Effect HIGH ENERGY, SHORT LIGHT PASSES EASILY THROUGH ATMOSPHERE CO MOLECULES ENERGY RELEASED AS HEAT LOWER ENERGY, LONGER LIGHT IS BLOCKED BY CO AND CH 4 ; ENERGY DOESN T ESCAPE INTO SPACE; ATMOSPHERE HEATS UP Energy fro Sun has short waelengths ( s) and high energy. CO and ethane (CH 4 ) let this light in. Reflected light has longer s and less energy. CO and CH 4 ( greenhouse gases ) preent reflected light fro escaping, thus waring the atosphere.

3 Why ore CO in atosphere now than 500 years ago? burning of fossil fuels deforestation -- coal -- urban sprawl -- petroleu -- wildlife areas -- natural gas -- rain forests -- wood * The burning of ethanol won t slow greenhouse effect. What can we do?. Reduce consuption of fossil fuels. At hoe: insulate hoe; run dishwasher full; aoid tep. extrees (A/C & furnace); wash clothes on war, not hot On the road: bike instead of drie; carpool; energy-efficient ehicles. Support enironental organizations. 3. Rely on alternate energy sources. solar, wind energy, hydroelectric power

4 The Kinetic Molecular Theory (KMT) -- explains why gases behae as they do -- deals w / ideal gas particles. are so sall that they are assued to hae zero olue. are in constant, straight-line otion 3. experience elastic collisions in which no energy is lost 4. hae no attractie or repulsie forces toward each other 5. hae an aerage kinetic energy (KE) that is proportional to the absolute tep. of gas (i.e., Kelin tep.) AS TEMP., KE Theory works, except at high pressures and low teps. **Two gases w /sae # of particles and at sae tep. and pressure hae the sae kinetic energy. KE is related to ass and elocity (KE = ½ ) To keep sae KE, as, ust OR as, ust

5 More assie gas particles are slower than less assie gas particles (on aerage). Particle-elocity Distribution (arious gases, sae T and P) # of particles CO N H (SLOW) elocity of particles (/s) Particle-elocity Distribution (sae gas, sae P, arious T) (FAST) # of particles 0 o C 50 o C 00 o C (SLOW) elocity of particles (/s) (FAST)

6 Graha s Law Consider two gases at sae tep. Gas : KE = ½ Gas : KE = ½ Since tep. is sae, then KE = KE ½ = ½ = Diide both sides by Take sq. rt. of both sides to get Graha s Law:

7 To use Graha s Law, both gases ust be at sae tep. diffusion: particle oeent fro high to low conc. NET MOEMENT effusion: diffusion of gas particles through an opening For gases, rates of diffusion & effusion obey Graha s law: ore assie = slow; less assie = fast On ag., carbon dioxide traels at 40 /s at 5 o C. Find ag. speed of chlorine at 5 o C. Cl CO CO Cl Cl CO CO Cl Cl 40 /s 44 g 7g 30 /s **Hint: Put whateer you re looking for in the nuerator.

8 At a certain tep., fluorine gas traels at 58 /s and a noble gas traels at 394 /s. What is the noble gas? F F F F F F 38 au au CH 4 oes.58 ties faster than which noble gas? Goerning relation: CH 4.58 Kr CH 4 CH 4.58 CH 4 (.58) CH 4 (.58) CH4 (.58) (6 au) 39.9 au Ar HCl and NH 3 are released at sae tie fro opposite ends of.0 horiz. tube. Where do gases eet? NH 3 HCl HCl NH 3.0 HCl NH NH HCl elocities are relatie; pick easy #s: DISTANCE = RATE x TIME.0 HCl dist. NH3 dist..000 t HCl NH t.000 /s.465 /s t s So HCl dist. =.000 /s (0.487 s) = 0.487

9 Gas Pressure Pressure occurs when a force is dispersed oer a gien surface area. P F A If F acts oer a large area F A = P But if F acts oer a sall area F A = P At sea leel, air pressure is standard pressure: at, 0.3 kpa, 760 Hg, 4.7 lb/in Find force of air pressure acting on a baseball field tarp 00 ft. 00 ft. A [ 00 ft in ft ].44 x 0 6 in F = P A = 4.7 lb/in (.44 x 0 6 in ) = x 0 7 lb. F x 0 7 lb. ton 000 lb. 0,000 tons Key: Gases exert pressure in all directions. Atospheric pressure changes with altitude: as altitude, pressure

10 baroeter: deice to easure air pressure ercury (Hg) acuu air pressure Bernoulli s Principle For a fluid traeling // to a surface: LIQUID OR GAS FAST-oing fluids exert LOW pressure SLOW- HIGH FAST SLOW LOW P HIGH P roof in hurricane FAST LOW P SLOW HIGH P

11 airplane wing / helicopter propeller FAST LOW P Resulting Forces (BERNOULLI S PRINCIPLE) SLOW HIGH P AIR PARTICLES (GRAITY) frisbee creeping shower curtain CURTAIN windows and high winds (e.g., tornadoes) FAST LOW P TALL BUILDING COLD SLOW HIGH P WARM FAST LOW P SLOW HIGH P WINDOWS BURST OUTWARDS

12 Pressure and Teperature STP (Standard Teperature and Pressure) standard teperature standard pressure 0 o C at 73 K 0.3 kpa 760 Hg Equations / Conersion Factors: K = o C + 73 o C = K 73 at = 0.3 kpa = 760 Hg Conert 5 o C to Kelin. K = o C + 73 = 5 o C + 73 = 98 K How any kpa is.37 at? X kpa.37 at 0.3 kpa at 38.8 kpa How any Hg is 3.5 kpa? X Hg 3.5 kpa 760 Hg 0.3 kpa 737 Hg

13 anoeter: easures the pressure of a confined gas AIR PRESSURE CONFINED GAS Hg HEIGHT DIFFERENCE Atospheric pressure is 96.5 kpa; ercury height difference is 33. Find confined gas pressure, in at. X at 96.5 kpa 33 Hg SMALL + HEIGHT = BIG 96.5 kpa + 33 Hg = X at 96.5 kpa at 0.3 kpa 33 Hg at 760 Hg X at at at = X at X =.6 at

14 The Ideal Gas Law P nr T P = pressure (in kpa) n = # of oles of gas (ol) = olue (in L or d 3 ) T = teperature (in K) R = uniersal gas constant = 8.34 L - kpa ol - K 3 g oxygen at 0 o C is under 0.3 kpa of pressure. Find saple s olue. T = 0 o C + 73 = 73 K n 3 g O ol O 3 g O.0 ol P n R T n R T P ol (8.34) (73) L 0.5 g carbon dioxide fills a 350 L container at 7 o C. Find pressure in Hg. T = 7 o C + 73 = 400 K = 0.35 L n 0.5 g CO ol CO 44 g CO ol P P n R T 54.0 kpa n R T (8.34) (400) P Hg 405 Hg 0.3 kpa 54.0 kpa

15 P,, T Relationships At constant P, as gas T, its., T,. Charles s Law At constant, as gas T, its P., T, P. Gay-Lussac s Law At constant T, as P on gas, its., P,. Boyle s Law The Cobined Gas Law P T P T P = pressure (any unit will work) = olue (any unit will work) T = teperature (ust be in Kelin) = initial conditions = final conditions

16 A gas has ol. 4. L at 0 kpa. If tep. is constant, find pres. of gas when ol. changes to.3 L. P T P T P 0 kpa (4. L) P (.3 L) P = 40.9 kpa P Original tep. and ol. of gas are 50 o C and 300 d 3. Final ol. is 00 d 3. Find final tep. in o C, assuing constant pressure. T = 50 o C + 73 = 43 K P T P T T T 300 d 43 K 3 00 d T 300 d 3 (T ) = 43 K (00 d 3 ) 4 K = 3 o C 3 A saple of ethane occupies 6 c 3 at 75 o C and 985 Hg. Find its ol. at STP. T = 75 o C + 73 = 98 K 3 P P 985 Hg(6 c ) 760 Hg ( ) T T 98 K 73 K 985 (6) (73) = 98 (760) = 5 c 3

17 Density of Gases Density forula for any substance: For a saple of gas, ass is constant, but pres. and/or tep. changes cause gas s ol. to change. Thus, its density will change, too. D ORIG. OL. NEW OL. If (due to P or T ), then D ORIG. OL. NEW OL. If (due to P or T ), then D Density of Gases Equation: P T D ** As always, T s ust be in K. P T D

18 A saple of gas has density 0.00 g/c 3 at 8 o C and 8 Hg. Find density at 3 o C and 548 Hg. T = 8 o C + 73 = 55 K T = 3 o C + 73 = 386 K P T D P T D 8 55 (0.00 ) (D ) 8(386)(D ) = 55(0.00)(548) D = 9.4 x 0 4 g/c 3 A gas has density 0.87 g/l at 30 o C and 3. kpa. Find density at STP. T = 30 o C + 73 = 303 K P T D P T D (0.87 ) (D ) 3.(73)(D ) = 303(0.87)(0.3) D = 0.75 g/l Find density of argon at STP. D 39.9 g.4 L.78 g L

19 Find density of nitrogen dioxide at 75 o C and at. D of STP D 46.0 g.4 L.05 g L T = 75 o C + 73 = 348 K P T D P T D 73 (.05) (D ) (348) (D ) = 73 (.05) (0.805) D =.9 g/l A gas has ass 54 g and density.5 g/l at 53 o C and 0.85 at. What ol. does saple occupy at STP? Find D at STP. T = 53 o C + 73 = 36 K P T D P T D (.5) 73 (D ) 0.85 (73) (D ) = 36 (.5) () D =.756 g/l Find ol. when gas has that density. D D 54 g.756 g/l 87.7 L

20 Dalton s Law of Partial Pressure In a gaseous ixture, a gas s partial pressure is the one the gas would exert if it were by itself in the container. The ole ratio in a ixture of gases deterines each gas s partial pressure. Total pressure of ixture (3.0 ol He and 4.0 ol Ne) is 97.4 kpa. Find partial pressure of each gas. P He 3 ol He 7 ol gas 97.4 kpa 4.7 kpa P Ne 4 ol Ne 7 ol gas 97.4 kpa 55.7 kpa Dalton s Law: the total pressure exerted by a ixture of gases is the su of all the partial pressures P Z = P A,Z + P B,Z +

21 80.0 g each of He, Ne, and Ar are in a container. The total pressure is 780 Hg. Find each gas s partial pressure. 80 ghe 80 gne ol 4 g ol 0 g 0 ol He 4 ol Ne Total: 6 ol gas P He = 0 / 6 of total P Ne = 4 / 6 of total 80 g Ar ol 40 g ol Ar P Ar = / 6 of total P He 600 Hg, P Ne 0 Hg, P Ar 60 Hg Dalton s Law: P Z = P A,Z + P B,Z + Two.0 L containers, A and B, contain gases under.0 and 4.0 at, respectiely. Both gases are forced into Container B. Find total pres. of ixture in B. A B P X X Z P X,Z A.0 at.0 L.0 at.0 L B 4.0 at.0 L 4.0 at Total = 6.0 at

22 Two.0 L containers, A and B, contain gases under.0 and 4.0 at, respectiely. Both gases are forced into Container Z ( w /ol..0 L). Find total pres. of ixture in Z. A B Z P X X Z P X,Z A.0 at.0 L.0 at.0 L B 4.0 at.0 L.0 at Total = 3.0 at Find total pressure of ixture in Container Z. A B C Z.3 L.6 L 3.8 L.3 L 3. at.4 at.7 at X at P X X Z P X,Z A 3. at.3 L.8 at B.4 at.6 L.3 L.6 at C.7 at 3.8 L 4.5 at Total = 7.9 at

23 Gas Stoichioetry Find ol. hydrogen gas ade when 38. g zinc react w /excess hydrochloric acid. Pres.=07.3 kpa; tep.= 88 o C. X Zn (s) + HCl (aq) ZnCl (aq) + H (g) 38. g Zn excess = X L H P = 07.3 kpa T = 88 o C *** ol Zn ol H ol H 38. g Zn ol H 65.4 g Zn ol Zn At STP, we d use.4 L per ol, but we aren t at STP. P n R T n R T P ol (8.34) (36) 07.3 What ass solid agnesiu is req d to react w /50 L carbon dioxide at.5 at and 77 o C to produce solid agnesiu oxide and solid carbon? P Mg (s) + CO (g) MgO (s) + C (s) 6.3 L X g Mg = 50 L 0.5 L P =.5 at 5.95 kpa T = 77 o C 350 K n R T n P R T 5.95 (0.50) 8.34(350) 0.03 ol CO X gmg 0.03 ol CO ol Mg ol CO 4.3 gmg ol Mg 0.63 gmg

24 apor Pressure -- a easure of the tendency for liquid particles to enter gas phase at a gien tep. -- a easure of stickiness of liquid particles to each other ore sticky less likely to aporize In general: LOW.p. not ery sticky ore likely to aporize In general: HIGH.p. NOT all liquids hae sae.p. at sae tep. PRESSURE (kpa) TEMPERATURE ( o C) CHLOROFORM ETHANOL WATER olatile substances eaporate easily (hae high.p. s). BOILING when apor pressure = confining pressure (usually fro atosphere)

25 At sea leel and 0 o C AIR PRESSURE (~00 kpa) APOR PRESSURE (~5 kpa) APOR PRESSURE (~0 kpa) ETHANOL WATER NET PRESSURE (~95 kpa) NET PRESSURE (~90 kpa) ETHANOL WATER

AP Chapter 5: Gases Name

AP Chapter 5: Gases Name Warm-Ups (Show your work for credit) Date 1. Date 2. Date 3. Date 4. Date 5. Date 6. Date 7. Date 8. AP Chapter 5: Gases 2 Warm-Ups (Show your work for credit) Date 1. Date 2.